Sound absorbing material and method of making the same



Oct. 10, 1933. 4

E. T. HERMANN Filed July 14. 1950.

SOUND ABSORBING MATERIAL AND METHOD OF MAKING THE SAME IN VEN TOR.L'hzvzesifflrmazza.

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rss PATENT OFFICE BOUND ABSORBING MATERIAL AND METHOD OF MAKING THE SAMEEarnest T. Hermann, Manhattan Beach, Calif. Application July 14, 1930..Serial No.467fl'l UNITED STA 6 Claims.

This invention relates to sound absorbing or acoustic material, andparticularly to material made in the form of tile, slabs,'or blocks,adapted for covering walls and ceilings of rooms and having the propertyof largely absorbing sound waves striking the same, so as to minimizereflection of sound back into the room as well as transmission of soundvtherethrough. The invention includes not only a novel form of suchmaterial, but also a 1 new and advantageous method of making the same.

The principal object of the invention is to produce shaped bodies ofsound-absorbent material such as above described, which have a maximumsound absorption property, may be manufactured at relatively low cost,possess great mechanical strength and durability, are absolutelyfireproof and not injured by heat,-are unaffected by water oratmospheric conditions of any kind, and may be easily applied to thewall or ceiling to be covered thereby.

A particular object of the invention is to produce a sound-absorbingtile consisting wholly of mineral or inorganic materials andconsequently non-combustible.

. A further object of the invention is to produce such a sound-absorbingtile consisting wholly of mineral materials and of such nature that itis not weakened or injured in any way by the action of heat to which itmay ordinarily be subjected in case of fire in the room or building inwhich it is placed. I

A'further object is to produce a sound-absorbing tile, of the type abovedescribed, provided substantially throughout with extensivelyintercommunicating voids opening through the surfaces thereof, or atleast through the surface which is to be exposed when placed in positionon I the wall or ceiling.

4o Afurther object of the invention is to produce a sound-absorbing tileconsisting of mineral particles of fairly uniform size, or within acertain range of sizes, bonded together by a ceramic bonding structureformed in place by the action 5 of heat on fusible. ceramic material,such ceramic bonding structure being present only in sufficient amountto coat the surfaces of the particles and secure adjacent particlestogether at their points of contact, while leaving the major portion ofthe voids between-the particles free and unobstructed. The use of aceramic bonding structure of this type provides great structuralstrength and protection against damage by fire, water, or atmosphericconditions, while leaving a sufficient intercommunicating porositythroughoutthe body of 1 material to produce a maximum amount of soundabsorption. Furthermore, a material of this type may be manufactured atlow cost, both from the standpoint of cost of materials required andfrom the standpoint of the operations required in the manufacturethereof. A particularly advantageous feature is that, in the heating orfiring operation, only the thin glaze-like ceramic coating onjtheaggregate particles need be fired,

v so that a much less prolonged heat treatment is required than when theentire mass requires sintering throughout, as is the case with mostceramic tile or other ceramic material.

Afuither object of the invention isto provide a sound-absorbent tile forwalls and ceilings, having advantageous properties of surface texture,color, and general appearance.

The sound-absorbing material of my invention comprises essentially ashaped body, which may be referred to as a tile, ofany suitable size andshape and consisting of mineral particles, preferably of more or lessuniform particle size, firmly bonded together 'by ceramic material of aglassy, glazed, or sintered nature confined substantially wholly to thesurfacesof the particles and the junctures or points of contacttherebetween, said body being provided substantially throughout withextensively intercommunicating voids or passages between the particlesthus coated and bonded together.

The particles preferably consist. of material of light weight and moreor less porous or vesicular in itself, such as pumice, volcanic ash orbressia, or vesicular basaltic rock. The use of a material of this kindnot only increases the sound-absorbent properties of the block or tile,but also mini mizes the weight thereof. The invention is not necessarilyrestricted tothese materials, but in its broader aspect includes the useof any mineral or inorganic particleshaving suitable strength andcohesion, and adapted to substantially retain their shape, size,strength and cohesion whenheated to the temperature required for fusingor sintering the ceramic bonding material. For ex- .ample, I may usecrushed stone, granite, furnace slag, or any combinations of any two ormore of the above mentionedmineral materials. v While I have stated thatthe particles are preferably of more or less uniform size, it will beunderstood that there is no definite limit of uniformity required. Ingeneral, the largerthe particles the larger willbe the voidstherebetween. Furthermore, a material having relatively large particlesand voids will be most efficient in absorbing sound of relatively lowfrequency or pitch, -.and a material having smaller particles and voidswill be most efficient in absorbing sound of higher frequency or pitch.The most advantageous sizeof particle to be used in any particular casewill, therefore, depend largely on the kind of sound, and particularlyon the pitch of the sound, which is to'be absorbed. For general use,where it is desired to absorb sounds of varying frequencies withapproximately uniform efllciency, it will be found advantageous toprovide some variation in the size of the particles and consequentlyinthe size of the voids. On the other hand, too great a variation insize is objectionable, for the reason that the smaller particles tend tofill up the voids between the larger particles and thus decrease thepercentage of sound absorption. The particular sizes to be used in anycase, and the breadth of range in size, should be determined by aconsideration of the above factors in the order of their relativeimportance. In general, the use of mineral particles varying from acertain minimum size to from one and one-half to three times that sizemay be found satisfactory, and it will be seen, therefore, thatextremely accurate screening is not required. For example, I may form arelatively'fine grained tile using particles of from 16 to 40 mesh, 5'medium grained tile using particles of from 4 to 8 or from 6 to 12 mesh,or a relatively coarse grained tile using particles of from 2 to 4 mesh.The above figures, however, are given by way of example only and are notto be understood as limiting or defining the scope of my invention.

The ceramic bonding material, which coats the surfaces of the particlesand secures the same together at their points of contact, may consist ofany glassy, sintered, or glaze-like material, produced by fusion orincipient fusion of suitable glaze-forming or frit materials adapted toform a strong, coherent bonding structure. Such glaze-forming or fritmaterials may consist of natural silicates or other fusible earthy ormineral materials, or mixtures of any such materials, or artificialfrits prepared by firing mixtures of such materials having the desiredcomposition so as to form a frit having the proper fusion temcated at 2,with open voids or passages therebetweenj'as shown at 3. This gives apleasing rough textured surface, which requires no further surfacetreatment of any kind. The appearance of the tile may be modified as toroughness of texture by selecting different sizes of particles, and maybe modified as to color, either by using mineral aggregate'particleswhich are either naturally or artificially colored, with a transparentor translucent glaze as a bonding agent, or by using a colored glaze orburned enamel as a bonding agent.

The latter method is considered preferable, because of the ease ofobtaining almost any desired color, with a glossy or lustrousappearance, and also because only the relatively thin coating of ceramicmaterial need be colored in that case, thus reducing the amount ofcoloring material required. Furthermore, different colored glazes may beused as bonding agent on different tiles, or on different parts of thesame tile, so as to give any desired mottled color effect.

The structure of the tile is better illustrated in the enlargedsectional view thereof shown in Fig. 3. The particles themselves, ofpumice or other mineral aggregate, are indicated at 5. The ceramicbonding agent coats the surfaces of these particles, as indicated at 6,and also bridges across between the particles adjacent the'points ofcontact thereof, as at 7. Between the particles are the voids 3, whichform continuous or intercommunicating passages extending through thethickness of the formed tile or body.

The method of making the above described acoustic tile comprises, ingeneral, mixing the mineral particles or aggregate, graded to anydesired size or range of sizes, with the bonding agent, consisting of amixture of water or other suitable liquid with a suitable powdered orfinely divided flux, frit, or other fusible material, and alsopreferably containing a small amount of temporary adhesive or binder,such as commonly used in the ceramic industry, for causing the bondingagent to stick together and to adhere to the surfaces of the particles;then molding or forming this mixture to the shape of the tile, block, orother body to be formed, and then burning or firing these formed bodiesat a temperature sufficient to fuse the bonding agent, or at least bringthe same to the point of incipient fusion, so as to cause the formationof a glaze or glass-like structure coating the surfaces of the particlesand bonding the same together at their points of contact, withoutcausing fusion or appreciable softening of the mineral particlesthemselves. By this method, therefore, the open or porous structureoriginally present in the body as formed or molded is maintained, whilea ceramic bonding structure is produced having sufficient mechanicalstrength to impart the necessary strength to the finished product.

The fusible bonding agent may consist of any suitable material, ormixture of materials, adapted to fuse at a fairly high temperature butbelow the fusion point of the mineral aggregate particles, for example atemperature between 800 and 1200 C. The bonding agent, furthermore,should preferably have a coefficient of expansion approximately equal,or somewhat greater than, that of the aggregate material. For example,the coefficient of cubical'expansion of pumice is approximately 2 10 perdegree centigrade; when using this material as an aggregate, I prefer touse a bonding agent having a coefficient of cubical expansion between 2and 4 l0 Such agent may be ground to any desired fineness and mixed withthe water or other liquid and with gum tragacanth, glue, casein, orother suitable temporary binder in any suitable proportions, forexample, 1 part of dry powdered bonding agent, 1 to 3 parts of water,and 1/20 to part of adhesive or binder.

The resulting paste or wet mix containing the bonding agent is mixedwith the mineral aggregate particles in any suitable proportions, forexample, 1 part of actual fusible bonding agent therein to from 3 to '7parts of mineral aggregate.

In general, the proportion of .bonding agent to aggregate should besufficient to coat the surfaces of the aggregate particles and providefirm bonds therebetween, but should not exceed the amount actuallyrequired for this purpose, so as to leave the maximum amount ofunobstructed, intercommunicating voids between the particles.

The temperature of firing will depend upon the bonding material used,but-should be substantially, or somewhat above, the fusion temperatureof such material and below the softening or fusion temperature oftheaggregate particles, and the firing should be continued for asufficient length of time to substantially completely fuse this materialtogether as above described. I have found for that, in mostcases,heating for about or minutes at the fusion temperature of the bondingmaterial is sumcient, but it will be understood that the invention isnot restricted to any par- 6 ticular time of heating. However, as abovestated,

the required timeof heating is, ingeneral, much less than would be thecase if the entire mass of aggregate had to be fused or sinte'redthroughout.

- therein,

Example No. I

A raw flux was used as bonding agent, having a fusing temperature ofabout 1080 C. (cone 03). This fiux consisted of the followingingredients:

Percent Feldspar 59.62 Whiting (calcium carbonate) 8.03 Zinc oxide 6.50Kaolin 13.81 Flint 12.04

The above ingredients were mixed and ground to about 100 mesh, and theground mixture was then mixed with water and gum tragacanth in theproportions of 100 parts of dry ingredients, 175 parts of water and 6parts of gum traga canth. This wet mixture was then thoroughly mixedwith an aggregate consisting of pumice grains or particles graded tobetween 6 and 12 mesh. The proportion of the wet bonding mixture ,to thepumice was such as to provide one part of the dry ceramic bondingmaterial above described by 5 parts of pumice by weight. The mixing maybe efiected by hand or in any suit: able mixing apparatus adapted toeffect uniform coating of the-pumice particles by the wet bondingmixture without seriously crushing the pumice particles, and should becontinued for a suflicient length of time to insure thorough andsubstantially uniform coating of all the pumice particles. The mixturewas then placed in molds under slight pressure sufficient to cause thesame to retain their shape when removed from the molds, and the shapedbodies were then removed from the molds and fired in a kiln atapproximately 1080 to 1100 C. for about ten to fifteen minutes.

Example No. II

A frit was first prepared having a fusing point of 945 to 975 C. (cone08-07). This frit was prepared from the following ingredients:

Parts by weight Borax 100 Soda ash 54 Potash feldspar 110 Flint 110Saltpeter 23 Fluorspar 13 Barium carbonate 25 Antimony oxide 25 Zincoxide 25 Cryolite 25 These ingredients were mixed, ground to about 50mesh, fused at 1200 0., broken up by dropping the same, while molten,into water, and then ground to about 100- mesh. 60 parts of thisprepared and ground frit material were mixed with 10 parts of chinaclay, 150 parts of water and 4 parts of gum tragacanth, and the wetmixture was then mixed with 350 parts of pumice particles of from 6 to12 mesh in size, molded as above described and burned at about 945 to975 C. for ten or fifteen minutes.

As an example of the use of a coloring mate-' rial to impart a color tothe glaze or ceramic material coating the aggregate particles, asuitable coloring agent, such as cobalt oxide, may be added in anydesired proportion, in making the second example above given, thisparticular agent imparting a bright blue color to the surface of thefinished material.

I claim:

1. A sound-absorbent material comprising mineral particles bondedtogether by a ceramic bonding structure, said bonding structure beingpresent only in suflicient amount to coat the surfaces of the particlesand to form bonds between adjacent particles at the points of contactthereof while leaving the major portion of the voids between theparticles free and unobstructed.

2. A sound-absorbing material comprising particles of vesicular mineralmaterial bonded together by a fused bonding material coating thesurfaces of the particles and providing bonds between adjacent particlesat the points of contact thereof, said sound-absorbing material beingprovided throughout with extensively intercommunicating voids betweensaid particles thus coated and bonded together.

3. A sound-absorbent material as set forth in claim 2, said coating offused bonding material containing an agent imparting color thereto.

4. A sound-absorbing material comprising a shaped body consisting ofmineral particles firmly bonded together by a fused bonding structureformed in place by the action of heat on fusible ceramic material andconfined substantially wholly to the surfaces of the particles and thejunctures therebetween, said body being provided substantiallythroughout withiextensively intercommunicating voids between theparticles thus coated and bonded together. 5. The method of makingsound-absorbing material which comprises mixing a mineral aggregate witha fusible ceramic bon'ding material in only sufficient quantity to coatthe particles of said aggregate, forming a shaped body from saidmixture, and heating said body to a sufiicient temperature to fuse saidbonding material.

6. The method of making sound-absorbing material which comprises mixinga fusible bonding material in finely divided form with water, mixingsaid wet mixture with particles of mineral material, forming a shapedbody from said mixture, and heating said body to a temperaturesufilcient to develop a ceramic bonding structure from said fusiblematerial covering and bonding together the mineral particles, saidmineral ma,-

terial being substantially infusible at said temperature and the bondingmaterial being used only in sufficient proportion to provide the saidbonding structure, while leaving substantially unobstructed andintercommunicating voids between the particles.

EARNEST T. HERMANN.

Hill

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